Thermoplastic composite

ABSTRACT

A method of making a flexible pipe layer, which method comprises: commingling polymer filaments and carbon fibre filaments to form an intimate mixture, forming yarns of the commingled filaments, forming the yarns into a tape, and applying the tape to a pipe body to form a flexible pipe layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/338,236, filed 29 Mar. 2019, which is a U.S. National Application ofPCT/GB2017/052918, filed Sep. 28, 2017, which claims priority toProvisional Patent Application GB 1616706.6, filed Sep. 30, 2016, thedisclosures of which are incorporated herein by reference in theirentirety.

FIELD

The present invention relates to a thermoplastic composite and a methodfor forming such a composite. In particular, but not exclusively, thepresent invention relates to a flexible pipe formed from thethermoplastic composite. The present invention also relates to a methodof making a flexible pipe layer.

BACKGROUND

Traditionally flexible pipe is utilised to transport production fluids,such as oil and/or gas and/or water, from one location to another.Flexible pipe is particularly useful for connecting a sub-sea location(which may be deep underwater) to a sea level location. Flexible pipe isgenerally formed as an assembly of a flexible pipe body and one or moreend fittings. The pipe body is typically formed as a combination oflayered materials that form a pressure-containing conduit. The pipestructure allows large deflections without causing bending stresses thatimpair the pipe's functionality over its lifetime. The pipe body isgenerally built up as a combined structure including metallic andpolymer layers.

Unbonded flexible pipe has been used for deep water (less than 3,300feet (1,005.84 metres)) and ultra-deep water (greater than 3,300 feet)developments. It is the increasing demand for oil which is causingexploration to occur at greater and greater depths where environmentalfactors are more extreme. For example in such deep and ultra-deep waterenvironments ocean floor temperature increases the risk of conveyedfluids cooling to a temperature that may lead to pipe blockage.Increased depths also increase the pressure associated with theenvironment in which the flexible pipe must operate.

In many known flexible pipe designs the pipe body includes one or morepressure armour layers. The primary load on such layers is formed fromradial forces. Pressure armour layers often have a specific crosssectional profile to interlock so as to be able to maintain and absorbradial forces resulting from outer or inner pressure on the pipe. Crosssectional profiles of the wound wires that prevent the pipe fromcollapsing or bursting as a result of pressure are sometimes calledpressure-resistant profiles. When pressure armour layers are formed fromhelically wound wires forming hoop components, the radial forces fromouter or inner pressure on the pipe cause the hoop components to expandor contract, putting a tensile load on the wires.

One way to improve the load response and thus performance of armourlayers is to manufacture the layers from thicker and stronger and thusmore robust materials. For example for pressure armour layers in whichthe layers are often formed from wound wires with adjacent windings inthe layer interlocking, manufacturing the wires from thicker materialresults in the strength increasing appropriately. However, as morematerial is used, the weight of the flexible pipe increases. Ultimatelythe weight of the flexible pipe can become a limiting factor in usingflexible pipe. Additionally manufacturing flexible pipe using thickerand thicker material increases material costs appreciably, which mayalso be a disadvantage.

BRIEF SUMMARY

The present inventors have developed a material that can be used to forman armour layer around the pipe. Unlike conventional armour layers thatare typically formed of wound, inter-locking metal wires, the newmaterial is based on a thermoplastic composite.

According to a first aspect of the present invention there is provided amethod of making a flexible pipe layer, which method comprisescommingling polymer filaments and carbon fibre filaments to form anintimate mixture, forming yarns of the commingled filaments, forming theyarns into a tape, and applying the tape to a pipe body to form aflexible pipe layer.

According to a further aspect of the present invention there is provideda thermoplastic composite comprising fluoropolymer filaments and carbonfibre filaments, wherein the fluoropolymer filaments and carbon fibrefilaments are commingled to form an intimate mixture, and wherein thefluoropolymer has a melt flow index (230° C./2.16 kg) in the range of 40to 80 g/10 min.

The thermoplastic composite described above may be formed into a tape.

According to a further aspect of the present invention, there is alsoprovided a flexible pipe comprising at least one pipe layer formed orobtainable from a tape of a composite as described above.

The present invention also provides a flexible pipe comprising a pipelayer that comprises a first region formed from a thermoplasticcomposite comprising a polymer and carbon fibre, wherein carbon fibre ispresent in a first concentration, and a second region formed either from(i) a thermoplastic composite comprising a polymer and carbon fibre,wherein carbon fibre is present in a second concentration, or (ii) apolymer composition consisting essentially of polymer.

According to yet another aspect of the present invention, there isprovided a method of making a thermoplastic composite as describedherein, which comprises commingling polymer filaments and carbon fibrefilaments to form an intimate mixture.

The commingled polymer filaments and carbon fibre filaments may beformed into a yarn. Several yarns may be arranged adjacent to oneanother to form an assembly of yarns, which is then compressed to form atape. The tape may be wound around a pipe body to form a tubular pipelayer. The tubular pipe layer may then be heated so as to melt thepolymer filaments around the carbon fibre filaments to form afluoropolymer matrix. The resulting structure may be a flexible pipelayer, for example, a pressure armour layer.

The present inventors have found that, by commingling polymer filamentsand carbon fibre filaments, an intimate mixture of polymer filaments andcarbon fibre filaments can be produced. Furthermore, by selecting apolymer having a particular melt flow index, for example a fluoropolymerhaving a melt flow index (230° C./2.16 kg) in the range of 40 to 80 g/10min, it is possible to achieve sufficient adhesion between the polymerand the carbon fibre. By improving both the dispersion of the carbonfibre throughout the polymer matrix and the adhesion between the carbonfibre and the polymer, the final mechanical properties of the resultingcomposite can be improved. The present invention, therefore, allows athermoplastic composite to be produced that can used to form a pressurearmour layer that has sufficient mechanical strength to maintain andabsorb the radial or axial forces on the flexible pipe. At the sametime, the composite is relatively light, for example, when compared tometal wires conventionally used to form armour layers, and specificallypressure armour layers in the prior art.

As described above, the commingled filaments may be formed into a yarn.Several yarns may be arranged adjacent to one another to form anassembly of yarns, which is then compressed to form a tape. By arrangingyarns having different carbon concentrations adjacent to one another, itis possible to produce a tape having regions having different carbonfibre concentrations. Such a tape may be wound round a pipe body to forma tubular layer and then heated to soften or melt the polymer around thecarbon fibre filaments. This allows a flexible pipe layer having regionscontaining different concentrations of carbon fibre as an integralstructure. The commingling technique, therefore, enables the mechanicalproperties of the pipe layer to be varied and controlled, throughdesign, as desired. The design aspect is important as variations in theconcentration of fibres in a composite may be inevitable usingconventional techniques, however these variations in concentration areeither or both un-intended or uncontrolled, and therefore cannot berelied upon for design purposes. A composite armour layer in accordancewith the current invention is therefore also a significant improvementin the technology of composite pipe design.

Polymer

Any suitable polymer may be used to form the thermoplastic composite ofthe present invention. In one embodiment, the polymer is afluoropolymer. Suitable fluoropolymers include perfluoroalkoxy alkanes(PFA), poly(ethene-co-tetrafluoroethene) (ETFE), polytetrafluoroethylene(PTFE), fluorinated ethylene propylene (FEP) and polyvinylidene fluoride(PVDF), or an alloy of at least two of these polymers. Preferably, thefluoropolymer is PVDF or an alloy comprising a PVDF. It will berecognised also by those skilled in the art that alternative polymersmay also be used as directed in accordance with the present invention.For example, non-fluoropolymer materials such as poly-ether-ether-ketone(PEEK) or polyamide (for instance PA-11 or PA-12) may also be used asthe matrix material of the composite layer, designed and manufacturedwith varying properties through and along the layer. In one embodiment,a combination of at least one fluoropolymer and at least onenon-fluoropolymer may be used.

Preferably, the polymer is a fluoropolymer which comprises ahomopolymer. Preferably the homopolymer is a grade of PVDF.

The fluoropolymer may have a melt flow rate (230° C./2.16 kg) in therange of 40 to 80 g/10 min, preferably, 50 to 75 g/10 min. In oneembodiment, the fluoropolymer has a melt flow index of 60 to 70 g/10min. Melt flow rate may be measured using ASTM D1238, ISO 1133.

The fluoropolymer or fluoropolymer alloy may have a density in the range1.5-2.1 g/cm3.

Other polymer types will of course have different melt flow rates anddensities appropriate for those materials. For example PEEK may have adensity of 1.1-1.5 g/cm3. The density of the polyamides may be in therange 0.9-1.5 g/cm3.

Carbon Fibre

The carbon fibre may have a tow size of 3000 to 12000.

Suitable carbon fibre filaments are sold under the trademark Toray T700or Mitsubishi Grafil 34 or HexTow AS4 or Tenax HTS 40.

Thermoplastic Composite

The thermoplastic composite comprises commingled polymer filaments andcarbon fibre filaments. Preferably, the polymer filaments may befluoropolymer filaments. The polymer filaments may form 30 to 95 weight%, preferably 40 to 65 weight % of the total weight of the polymerfilaments and carbon fibre filaments in the composite. In oneembodiment, the polymer filaments form 45 to 60 weight %, preferably 50to 55 weight % of the total weight of the polymer filaments and thecarbon fibre filaments.

The commingled filaments may be formed by agitating the fibres atfilament level with a compressed gas(es), for example, compressed air.This may result in the formation of a single end roving of intimatelymixed or commingled fibres. Alternatively, the commingling may beperformed using a series of combs arranged to mix the fibres.

Once commingled, the fibres may form a yarn. The yarn may be compressedor extruded (or pultruded) to form a tape of the thermoplasticcomposite. The tape may be wrapped around a pipe body to form a tubularlayer. The tubular layer may then be heated to produce a flexible pipelayer, which may be used e.g. as a pressure armour layer in a flexiblepipe.

In one embodiment, a flexible pipe layer is produced that has regionshaving different concentrations of carbon fibre. This may be useful ifit is desirable to vary the mechanical properties of the pipe, forexample, along its length or radius. For example, the pipe may have oneor more regions in which carbon fibre is absent. Alternatively, the pipemay have one or more regions in which the carbon fibre concentration ishigher than in other regions of the pipe.

In one embodiment, a tape is produced which has regions having differentconcentrations of carbon fibre. For example, such a tape may be producedby arranging a first region of yarns having a first concentration ofcarbon fibre adjacent to a second region of yarns having a secondconcentration of carbon fibre, and compressing or extruding orpultruding the yarns to form a tape, whereby the tape has a first regionhaving a first concentration of carbon fibre, and a second region havinga second concentration of carbon fibre. Such a tape may be wound arounda pipe body to produce a tubular layer. When such a tubular layer isheated, the polymer may soften or melt to produce a flexible pipe layer.

In one embodiment, either the first region or second region of yarns maycontain no carbon fibre. Accordingly, the resulting tape and theeventual flexible pipe layer may contain one or more regions that aredevoid of carbon fibre.

In one embodiment the tape comprising fibre yarns may be wound around apipe body when only partially consolidated, subsequently the layer isconsolidated using heat and applied pressure as necessary once arrangedon the pipe body.

In one embodiment the tape comprising fibre yarns may be wound around apipe body before any consolidation is performed; all consolidation ofthe composite being applied, using heat and pressure as necessary, tothe comingled fibres arranged on the pipe body.

The flexible pipe layer formed using the thermoplastic composite of thepresent invention may be positioned adjacent (e.g. in contact with) atubular polymer layer. In one embodiment, the tubular polymer layer ispresent on the inside of the flexible pipe layer formed using thethermoplastic composite of the present invention. The tubular polymerlayer may be an extruded thermoplastic barrier layer. The thermoplasticbarrier layer may comprise, for example, a fluoropolymer or polyamide.An example of fluoropolymer for the thermoplastic barrier layer ispolyvinylidene fluoride. An example of a suitable polyamide is Nylon® 11(Arkema®). The thermoplastic barrier layer may be used as the pipe bodyaround which a tape formed from the thermoplastic composite of thepresent invention is wound.

Additionally or alternatively, a tubular polymer layer may comprisemultiple sub-layers of one or more polymer types or alloys, provided theouter sub-layer onto which the thermoplastic composite layer is appliedis compatible with or the same as the thermoplastic polymer of thecomposite layer.

Additionally or alternatively, a tubular polymer layer may be of amaterial incompatible with the thermoplastic of the composite layer andrequire a tie-in layer between the two. That tie-in layer may comprise adifferent type of polymer, such as an epoxy material or may itselfcomprise a composite a matrix material with filler particles therein, asdescribed in WO 2015/118356.

Additionally or alternatively, a tubular polymer layer may be positionedon the outside of the flexible pipe layer formed using the thermoplasticcomposite of the present invention. For example, the tubular polymerlayer may be extruded onto the outside of the flexible pipe layer formedusing the thermoplastic composite of the present invention as ananti-wear layer. The tubular polymer layer may be a thermoplastic layer.The layer may be formed of a polyamide, for example, Nylon® 11(Arkema®).

A tensile strength layer may be wrapped around the anti-wear layer.Suitable tensile strength layers may be formed of metal wires or acomposite, for example, a composite according to the present invention,or a composite comprising carbon fibres in a thermoset polymer matrix.

The thermoplastic composite may have an air bubble void content of lessthan 5% and preferably less than 2% by volume. This may be determinedusing standard density measurements and combining this withthermo-gravimetric analysis testing. An alternative method is toestimate the volume fraction of fibres using optical microscopy on aseries of cross sections of the composites. ASTM D2734 is a furtheralternative method based on density measurement.

The thermoplastic composite may contain additives. Suitable additivesinclude may include maleic anhydride which may be added to the polymermatrix at various stages in the manufacturing process for the polymerfilaments. Alternatively additives such as those to improve UVresistance or abrasion resistance or friction characteristics of thematerial may be added, for example carbon black, nano-clays, titaniumoxide etc. Such additives may be added to the thermoplastic compositeprior to forming a tape, or prior to heating the tape to form a tubularlayer. Alternatively, such additives may be incorporated into thepolymer filaments and may be present in the polymer filaments prior tocommingling the polymer filaments with the carbon fibre filaments.

LISTING OF FIGURES

Embodiments of the invention are further described hereinafter withreference to the accompanying drawings, in which:

FIG. 1 illustrates a flexible pipe body; and

FIG. 2 illustrates a riser, flowline and jumper.

In the drawings like reference numerals refer to like parts.

DETAILED DESCRIPTION

Throughout this description, reference will be made to a flexible pipe.It will be understood that a flexible pipe is an assembly of a portionof pipe body and one or more end fittings in each of which a respectiveend of the pipe body is terminated. FIG. 1 illustrates how pipe body 100is formed in accordance with an embodiment of the present invention froma combination of layered materials that form a pressure-containingconduit. Although a number of particular layers are illustrated in FIG.1 , it is to be understood that the present invention is broadlyapplicable to coaxial pipe body structures including two or more layersmanufactured from a variety of possible materials. For example, the pipebody may be formed from polymer layers, metallic layers, compositelayers, or a combination of different materials. It is to be furthernoted that the layer thicknesses are shown for illustrative purposesonly.

As illustrated in FIG. 1 , a pipe body includes an optional innermostcarcass layer 101. The carcass provides an interlocked construction thatcan be used as the innermost layer to prevent, totally or partially,collapse of an internal pressure sheath 102 due to pipe decompression,external pressure, and tensile armour pressure and mechanical crushingloads. The carcass layer is often a metallic layer, formed fromstainless steel, for example. The carcass layer could also be formedfrom composite, polymer, or other material, or a combination ofmaterials. It will be appreciated that certain embodiments of thepresent invention are applicable to ‘smooth bore’ operations (i.e.without a carcass layer) as well as such ‘rough bore’ applications (witha carcass layer).

The internal pressure sheath 102 acts as a fluid retaining layer andcomprises a polymer layer that ensures internal fluid integrity. It isto be understood that this layer may itself comprise a number ofsub-layers. It will be appreciated that when the optional carcass layeris utilised the internal pressure sheath is often referred to by thoseskilled in the art as a barrier layer. In operation without such acarcass (so-called smooth bore operation) the internal pressure sheathmay be referred to as a liner.

A pressure armour layer 103 is a structural layer that increases theresistance of the flexible pipe to internal and external pressure andmechanical crushing loads. The layer also structurally supports theinternal pressure sheath. In a preferred embodiment, the pressure armourlayer 103 is formed from the thermoplastic composite described herein.

The flexible pipe body also includes an optional first tensile armourlayer 105 and optional second tensile armour layer 106. Each tensilearmour layer is used to sustain tensile loads and internal pressure. Thetensile armour layer is often formed from a plurality of (e.g. metallic)wires (to impart strength to the layer) that are located over an innerlayer and are helically wound along the length of the pipe at a layangle typically between about 10° to 55°. The tensile armour layers areoften counter-wound in pairs. The tensile armour layers are oftenmetallic layers, formed from carbon steel, for example. The tensilearmour layers could also be formed from composite, polymer, or othermaterial, or a combination of materials.

The flexible pipe body shown also includes optional layers of tape 104which help contain underlying layers and to some extent prevent abrasionbetween adjacent layers, or indeed as an outer surface of the flexiblepipe in areas which may experience abrasion during service. The tapelayer may be a polymer or composite or a combination of materials. Thetape layer 104 may be formed of the thermoplastic composite describedherein.

The flexible pipe body also typically includes optional layers ofinsulation 107 and an outer sheath 108, which comprises a polymer layerused to protect the pipe against penetration of seawater and otherexternal environments, corrosion, abrasion and mechanical damage.

Each flexible pipe comprises at least one portion, sometimes referred toas a segment or section of pipe body 100 together with an end fittinglocated at at least one end of the flexible pipe. An end fittingprovides a mechanical device which forms the transition between theflexible pipe body and a connector. The different pipe layers as shown,for example, in FIG. 1 are terminated in the end fitting in such a wayas to transfer the load between the flexible pipe and the connector.

FIG. 2 illustrates a riser assembly 200 suitable for transportingproduction fluid such as oil and/or gas and/or water from a sub-sealocation 201 to a floating facility. For example, in FIG. 2 the sub-sealocation 201 includes a sub-sea flow line. The flexible flow line 205comprises a flexible pipe, wholly or in part, resting on the sea floor204 or buried below the sea floor and used in a static application. Thefloating facility may be provided by a platform and/or buoy or, asillustrated in FIG. 2 , a ship 200. The riser assembly 200 is providedas a flexible riser, that is to say a flexible pipe 203 connecting theship to the sea floor installation. The flexible pipe may be in segmentsof flexible pipe body with connecting end fittings.

It will be appreciated that there are different types of riser, as iswell-known by those skilled in the art. Embodiments of the presentinvention may be used with any type of riser, such as a freely suspended(free, catenary riser), a riser restrained to some extent (buoys,chains), totally restrained riser or enclosed in a tube (I or J tubes).

FIG. 2 also illustrates how portions of flexible pipe can be utilised asa flow line 205 or jumper 206.

It will be clear to a person skilled in the art that features describedin relation to any of the embodiments described above can be applicableinterchangeably between the different embodiments. The embodimentsdescribed above are examples to illustrate various features of theinvention.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of them mean “including but notlimited to”, and they are not intended to (and do not) exclude othermoieties, additives, components, integers or steps. Throughout thedescription and claims of this specification, the singular encompassesthe plural unless the context otherwise requires. In particular, wherethe indefinite article is used, the specification is to be understood ascontemplating plurality as well as singularity, unless the contextrequires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith. All of the features disclosed in this specification(including any accompanying claims, abstract and drawings), and/or allof the steps of any method or process so disclosed, may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. The invention is notrestricted to the details of any foregoing embodiments. The inventionextends to any novel one, or any novel combination, of the featuresdisclosed in this specification (including any accompanying claims,abstract and drawings), or to any novel one, or any novel combination,of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which arefiled concurrently with or previous to this specification in connectionwith this application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

1. A flexible pipe, comprising: a pipe layer that comprises: a firstregion characterized by a thermoplastic composite comprising a polymerand carbon fibre, wherein carbon fibre is present in a firstconcentration, and a second region characterized by one or more of: athermoplastic composite comprising a polymer and carbon fibre, whereincarbon fibre is present in a second concentration; and a polymercomposition.
 2. The flexible pipe of claim 1, wherein the firstconcentration of carbon fibre and the second concentration of carbonfibre are set by an application of tapes respectively to the firstregion and the second region.
 3. The flexible pipe of claim 1, whereinthe polymer is a fluoropolymer having a melt flow index (230° C./2.16kg) in the range of 50 to 80 g/10 min wherein the fluoropolymer isselected from at least one of perfluoroalkoxy alkanes (PFA),poly(ethene-co-tetrafluoroethene) (ETFE), polytetrafluoroethylene(PTFE), fluorinated ethylene propylene (FEP) and polyvinylidene fluoride(PVDF).
 4. The flexible pipe of claim 1, wherein the polymer is afluoropolymer having a melt flow index (230° C./2.16 kg) in the range of60 to 70 g/10 min, wherein the fluoropolymer is selected from at leastone of perfluoroalkoxy alkanes (PFA), poly(ethene-co-tetrafluoroethene)(ETFE), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene(FEP) and polyvinylidene fluoride (PVDF).
 5. The flexible pipe of claim1, wherein the carbon fibre has a tow size of 3000 to
 12000. 6. Theflexible pipe of claim 1, wherein the polymer is poly-ether-ether-ketone(PEEK) or polyamide (PA-11 or PA-12).
 7. The flexible pipe of claim 1,wherein the polymer is present in an amount of 30 to 70 weight % of thetotal weight of the polymer and carbon fibre in either the first region,or the second region, or both of the first and second region.
 8. Theflexible pipe of claim 1, wherein the pipe layer comprises a pressurearmour layer positioned adjacent to, or bonded to, a tubular polymerlayer.
 9. The flexible pipe of claim 8, wherein the tubular polymerlayer is disposed on an inside portion of the pressure armour layer andis configured as a fluid barrier layer.
 10. A method of manufacturing aflexible pipe layer, the method comprising: commingling polymerfilaments and carbon fibre filaments to form an intimate mixture;forming yarns from the intimate mixture; forming tape from the yarns;and forming a flexible pipe layer by applying the tape to a pipe body.11. The method of claim 10, wherein commingling the polymer filamentsand carbon fibre filaments comprises applying a compressed gas to thepolymer filaments and carbon fibre filaments to form the intimatemixture of the filaments.
 12. The method of claim 10, whereincommingling the polymer filaments and carbon fibre filaments comprisesapplying a series of combs to the polymer filaments and carbon fibrefilaments to form the intimate mixture of the filaments.
 13. The methodof claim 10, wherein forming the tape from the yarns comprisescompressing or extruding one or more of the filaments and the yarns. 14.The method of claim 10, further comprising: arranging a first region offilaments or yarns having a first concentration of carbon fibre adjacentto a second region of filaments or yarns having a second concentrationof carbon fibre; and compressing or extruding one or more of thefilaments and the yarns to form a tape, wherein the tape ischaracterized by a first region having a first concentration of carbonfibre, and a second region having a second concentration of carbonfibre.
 15. The method of claim 10, further comprising; arranging a firstregion of filaments or yarns that contain carbon fibre adjacent to asecond region of filaments or yarns consisting essentially of polymer;and compressing or extruding the filaments or yarns to form a tape,wherein the tape is characterized by a first region containing carbonfibre, and a second region consisting essentially of polymer.
 16. Themethod of claim 10, further comprising: arranging a first plurality offilaments or yarns having a first concentration of carbon fibre, thearranging comprising: commingling polymer filaments and carbon fibrefilaments to form a first intimate mixture, forming first yarns from thefirst intimate mixture, compressing or extruding first yarns to form afirst tape, wherein the first tape is characterized by a firstconcentration of carbon fibre, and arranging a second plurality offilaments or yarns having a second concentration of carbon fibre, thearranging comprising: commingling polymer filaments and carbon fibrefilaments to form a second intimate mixture, forming second yarns fromthe second intimate mixture, compressing or extruding the second yarnsto form a second tape, wherein the second tape is characterized by asecond concentration of carbon fibre, and applying predetermined amountsof the first tape and the second tape to a pipe body to form a flexiblepipe layer.
 17. The method of claim 10, further comprising wrapping thetape around a pipe body, and heating the wrapped tape so that thepolymer filaments melt around the carbon filaments to form a polymermatrix.
 18. The method of claim 10, wherein the polymer filamentscomprise a fluoropolymer, and wherein the polymer has a melt flow index(230° C./2.16 kg) in the range of 50 to 80 g/10 min.
 19. The method ofclaim 10, wherein the polymer filaments comprise a fluoropolymer, andwherein the polymer has a melt flow index (230° C./2.16 kg) in the rangeof 60 to 70 g/10 min.
 20. The method of claim 10, further comprisingforming a pressure armour layer on the pipe body.